Editing Flat-twelve engine (section)

=== Sports car racing ===
{{Listen|filename=Porsche 917 40th Anniversary.ogg|title=Porsche 917 flat-12|description=Eleven 917s pull away at Goodwood Festival of Speed 2009}}
In 1969, the [[Porsche 917]] sports prototype racing car introduced an air-cooled flat-twelve engine. This flat-twelve engine was based on the previous flat-eight engine, but it used a V12 crankshaft configuration instead of the [[boxer engine|boxer]] configuration used by the flat-eight. The domination of the Porsche 917 probably influenced Ferrari, because they switched from V12 engines to flat-twelve engines (using a boxer configuration) for the [[Ferrari 312 PB]], which competed from 1971 to 1973. Alfa Romeo also used flat-twelve engines in the 1973-1976 [[Alfa Romeo Tipo 33#Alfa Romeo 33TT12|Alfa Romeo 33TT12]] and [[Alfa Romeo Tipo 33#Alfa Romeo 33SC12|Alfa Romeo 33SC12]] sports prototype racing cars.

For the 1991 sports-prototype racing category, Mercedes-Benz switched from a twin-turbo V8 engine to a naturally-aspirated flat-twelve engine for in the [[Mercedes-Benz C291]] racing car. This engine employed a cylinder-head design with exhaust ports where the intake ports would normally be (on top of the engine, pointing upwards). The intake ports are between the intake and exhaust camshafts, just above the spark-plugs, pointing at an outward angle from the vertical. This was done to allow the engine to be installed lower in the chassis. The C291 was unsuccessful and Mercedes withdrew from sports-prototype racing after the 1991 season.